- Correlation of Alkyl and Polar Groups in the Gas-Phase Pyrolysis Kinetics of α-Substituted Ethyl Chlorides
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The kinetics of the gas-phase pyrolysis of several secondary chlorides were determined in a static system over the temperature range 369.9-490.1 deg C and the pressure range of 28-298 Torr.The reactions in seasoned vessels, with the free radical suppressor propene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law.The observed rate coefficients are represented by the following Arrhenius equations: for 2-chloropropionitrile, log k1 (s-1) = (13.45+/-0.57)-(236.1+/-8.2) kJ mol-1; for methyl 2-chloropropionate, log k1 (s-1) = (12.22+/-0.54) - (217.0+/-7.4) kJ mol-1 (2.303RT)-1; for methyl 3-chlorobutyrate, log k-1 (s-1) = (13.65 +/-0.39)-(214.9+/-5.0) kJ mol-1 (2.303RT)-1.The data of this work together with those reported in the literature confirm previous correlations that α-alkyl substituents of ethyl chloride give a good straight line, when log k/k0 vs. ?* values (ρ* = -3.58 +/- 0.24, correlation coefficient = 0.996, and intercept = -0.0066 at 360 deg C) are plotted, while α-polar substituents give rise to an inflection point at ?*(CH3) = 0.00 into another straight line (ρ* = -0.46+/-0.06, correlation coefficient = 0.972, and intercept = 0.017 at 360 deg C).Several other polar α-substituents have been found to enhance the dehydrochlorination process by means of their electron delocalization or resonance effect.Revising a work reported on the pyrolysis kinetics of pinacolyl chloride, a Wagner-Meerwein rearrangement appears to be a reasonable explanation for the formation of about 12percent of the 2,3-dimethylbutene products.
- Dominguez, Rosa M.,Rotinov, Alexandra,Chuchani, Gabriel
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- Stereospecific synthesis of EET metabolites via Suzuki-Miyaura coupling
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Bioactive, chain-shortened EET metabolites, viz. 8,9-epoxytetradec-5(Z)-enoic acid and 9,10-epoxyoctadec-6(Z),12(Z)-dienoic acid, were prepared via Suzuki-Miyaura cross-couplings of n-alkylboronic acids with chiral vinyl iodides.
- Falck,Kumar, P. Srinagesh,Reddy, Y. Krishna,Zou, Gang,Capdevila, Jorge H.
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- The flash vacuum thermolysis of (-)-cocaine
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(-)-Cocaine is thermally labile and, in a series of remarkable thermal reactions, is cleanly partitioned among benzoic acid, N-methylpyrrole and methyl 3-butenoate.
- Sisti,Fowler,Fowler
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Read Online
- (Ferrocenylpyrazolyl)palladium(II) complexes: Syntheses, characterization and rearrangement in solution
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Reactions of L1-L6 (3-ferrocenylpyrazolyle (L1), 3-ferrocenyl-5-methylpyrazolyle (L2) 3-ferrocenylpyrazolyl-methylenepyridine (L3) and 3-ferrocenyl-5-methylpyrazolylmethylene-pyridine (L4), 3-ferrocenylpyrazolylethylamine (L5) and 3-ferrocenyl-5-methylpyrazolylethyl-amine (L6)) with [PdCl(Me) (cod)] formed the mononuclear complexes [PdCl(Me) (κ1-L1)2] (1), [PdCl(Me) (κ1-L2)2] (2), [PdCl(Me) (κ2-L3)] (3), [PdCl(Me) (κ2-L4)] (4), [PdCl(Me) (κ2-L5)] (5) and [PdCl(Me) (κ2-L6)] (6). Reactions of 1-6 with the halide abstractor, Na[BAr4], (Ar = 3,5-(CF3)2C6H3), led to the formation of the salts, [PdMe(NCMe) (κ1-L1)2][BAr4] (7), [PdMe(NCMe) (κ1-L2)2][BAr4] (8), [PdMe(NCMe) (κ2-L3)][BAr4] (9), [PdMe(NCMe) (κ2-L4)][BAr4] (10), [PdMe(NCMe) (κ2-L5)][BAr4] (11), [PdMe(NCMe) (κ2-L6)][BAr4] (12) respectively. However, when 3 or 4 was reacted with of Na[BAr4] and a slight excess of methyl acrylate, the products were surprisingly the bis(ligand)palladium complexes [Pd(κ2-L3)2][BAr4]2 (13) and [Pd(κ2-L4)2][BAr4]2 (14) instead of the expected acylpalladium chelate complexes ([(κ2-L)Pd{(CH2)2C(O)OMe}][BAr4]). Complexes 1-6, activated with Na[BAr4], and pre-activated complexes 7-12 at 10 bar of ethylene and 30 bar of carbon monoxide produced polyketones, albeit with low activity (ca. 1.00 g.mmol-1Pd.h-1); with the active catalysts rearranging to mainly bis(pyrazolyl)palladium complexes similar to 13 and 14.
- Obuah, Collins,Darkwa, James
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- Stereoselective Total Synthesis of the Dimeric Naphthoquinonopyrano-?-lactone (-)-Crisamicin A: Introducing the Dimerization Site by a Late-Stage Hartwig Borylation
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The first stereoselective total synthesis of the dimeric naphthoquinonopyrano-?-lactone (-)-crisamicin A was realized (13 steps, 5% overall yield). 1,4,5-Trimethoxynaphthalene, reached in five known steps, was brominated at C-3 to install a but-3-enoic ester by an ensuing Heck coupling. An asymmetric Sharpless dihydroxylation followed and gave a β-hydroxy-?-lactone with >99.9% ee. Its OH substituent and acetaldehyde established the dihydropyran ring in a completely diastereoselective oxa-Pictet-Spengler cyclization. The 2,3-fused anisole moiety allowed the C5-H bond under Hartwig's conditions to be borylated. This set the stage for engaging the resulting C5-B bond in an oxidative dimerization, which led to a binaphthohydroquinon-5-yl. The latter was advanced to synthetic crisamicin A by a double CAN oxidation (→ a binaphthoquinon-5-yl) and a double demethylation.
- Brückner, Reinhard,Kopp, Julia
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supporting information
(2020/05/05)
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- Deoxygenation of Epoxides with Carbon Monoxide
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The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
- Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
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p. 10634 - 10640
(2020/07/30)
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- Nickel-Catalyzed Alkyl-Alkyl Cross-Electrophile Coupling Reaction of 1,3-Dimesylates for the Synthesis of Alkylcyclopropanes
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Cross-electrophile coupling reactions of two Csp3-X bonds remain challenging. Herein we report an intramolecular nickel-catalyzed cross-electrophile coupling reaction of 1,3-diol derivatives. Notably, this transformation is utilized to synthesize a range of mono- and 1,2-disubstituted alkylcyclopropanes, including those derived from terpenes, steroids, and aldol products. Additionally, enantioenriched cyclopropanes are synthesized from the products of proline-catalyzed and Evans aldol reactions. A procedure for direct transformation of 1,3-diols to cyclopropanes is also described. Calculations and experimental data are consistent with a nickel-catalyzed mechanism that begins with stereoablative oxidative addition at the secondary center.
- Chen, Pan-Pan,Hong, Xin,Jarvo, Elizabeth R.,McGinnis, Tristan M.,Sanford, Amberly B.,Thane, Taylor A.
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supporting information
(2020/03/23)
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- Synthesis of 2-Fluoroacetoacetic Acid and 4-Fluoro-3-hydroxybutyric Acid
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The butyric acid scaffold is the base structure of several human metabolites that serve diverse and prominent biochemical roles including as oxidative sources of cellular energy and as substrates for biosynthesis. Derivatization of metabolites through incorporation of fluorine often alters bioactivity and can facilitate detection and analysis by nuclear magnetic resonance or positron emission tomography depending upon the fluorine isotope employed. We describe the synthesis of two new fluorinated butyric acids (and three related esters) that are derivatives of the metabolites acetoacetic acid and 3-hydroxybutyric acid. 4-Fluoro-3-hydroxybutyric acid is prepared from epoxy ester precursors via ring opening by triethylamine trihydrofluoride. 2-Fluoroacetoacetic acid is prepared by electrophilic fluorination of an acid-labile β-keto ester. The gradual pH-dependent decarboxylation of 2-fluoroacetoacetic acid is investigated by 19 F NMR spectroscopy.
- Mattingly, Stephanie J.,Wuest, Frank,Schirrmacher, Ralf
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supporting information
p. 2351 - 2358
(2019/05/24)
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- PROCESS FOR PREPARING MONO AND DICARBOXYLIC ACIDS
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The present application relates to a process for preparing a dicarboxylic acid or dicarboxylic ester according to general formula (IV) R1OOC-(CH2)m-CH2CH2-(CH2)y-COOR4 (IV), comprising the steps of subjecting alkenoic acid or alkenoate of formula (II) R1OOC-(CH2)m-CH=CH-(CH2)x-H (II) to a metathesis reaction in the presence of a metathesis catalyst to form a longer-chain alkenoic acid or alkenoate of formula (III) R1OOC-(CH2)m-CH=CH-(CH2)y-H (III) where xa carbonylation reaction in the presence of a carbonylation catalyst and a carbonyl source to form said compound of Formula (IV). Alternative embodiments provide: a process for preparing an alkenoic acid or alkenoate comprising the step of subjecting a lactone to a ring opening reaction; a process for preparing a monocarboxylic acid or monocarboxylic ester according to general formula (XI) R1OOC-(CH2)m-CH2-(CH2)y-CH3 (XI) by subjecting an alkenoic acid or alkenoate to alkene hydrogenation; and a process for preparing an alcohol or ether according to general formula (XII) R1O-CH2-(CH2)m-CH2-(CH2)y-CH3 (XII) by subjecting an alkenoic acid or alkenoate to hydrogenation. The use of the respective mono/dicarboxylic acid, mono/dicarboxylic ester, ethers or alcohols in a variety of applications is also disclosed.
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Page/Page column 33; 34
(2018/02/03)
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- Dimethyl malonate/LHMDS system as a new protocol for generating methyl formate anion (-COOMe) in the condensed-phase Dedicated to Professor Charles H. DePuy (1927-2013)
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The treatment of dimethyl malonate with LHMDS in anhydrous THF (condensed-phase) generates, in addition to the expected corresponding lithium enolate, methyl formate anion (or methoxycarbonyl anion, -COOMe) which can react with several electrophiles to give corresponding methoxycarbonyl derivatives by nucleophilic substitution reaction.
- Di Bussolo, Valeria,Princiotto, Salvatore,Martinelli, Elisa,Bordoni, Vittorio,Crotti, Paolo
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supporting information
p. 1644 - 1647
(2016/04/04)
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- Liberation of methyl acrylate from metallalactone complexes via M-O ring opening (M = Ni, Pd) with methylation agents
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Ring opening of various nickela- and palladalactones induced by the cleavage of the M-O bond by methyl trifluoromethanesulfonate (MeOTf) and methyl iodide (MeI) is examined. Experimental evidence supports the mechanism of ring opening by the alkylating agent followed by β-H elimination leading to methyl acrylate and a metal-hydride species. MeOTf shows by far higher efficiency in the lactone ring opening than any other methylating agent including the previously reported methyl iodide.
- Lee, S. Y. Tina,Ghani, Amylia Abdul,D'Elia, Valerio,Cokoja, Mirza,Herrmann, Wolfgang A.,Basset, Jean-Marie,Kuehn, Fritz E.
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supporting information
p. 3512 - 3517
(2013/11/06)
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- Total regio- and diastereocontrol in the aldol reactions of dienolborinates
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It is reported that appropriate dienolborinates can provide access to both diastereomers of 2-(hydroxymethyl)but-3-enoates through exclusive α-regiocontrol in a non-vinylogous pathway. Contrary to previous reports in which dialkylchloroboranes failed to enolize propanoates, acidity-enhanced but-3-enoates readily undergo enolization, offering unprecedented control over the formation of these valuable synthons. The first example of an aldol reaction in the presence of a phosphine-borane adduct is also reported.
- Ramachandran, P. Veeraraghavan,Nicponski, Daniel,Kim, Bomi
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supporting information
p. 1398 - 1401
(2013/05/09)
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- Substituent effects of the backbone in α-diimine palladium catalysts on homo- and copolymerization of ethylene with methyl acrylate
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On the basis of different approaches for modifying α-diimine palladium catalysts, a series of methyl chloride palladium complexes with various α-diimine ligand backbones were synthesized and characterized. The corresponding cationic palladium complex chelating esters were further obtained by treatment of methyl chloride palladium complexes with methyl acrylate (MA). It was observed that decomposition of a cationic palladium complex chelating ester can occur to produce a new cationic palladium complex chelating two ligands and two counteranions, which provides a new pathway for deactivation of palladium catalysts and formation of palladium black by a fragmentation pattern with ester loss. These α-diimine palladium catalysts were employed in the homopolymerization of ethylene and copolymerization of ethylene and MA to evaluate substituent effects of the ligand backbone. A bulky camphyl α-diimine palladium catalyst was found to show better thermal stability and afford high-molecular-weight copolymer with higher incorporation of polar monomer. Longstanding living polymerization of ethylene was also achieved within 12 h using a bulky camphyl α-diimine palladium catalyst.
- Guo, Lihua,Gao, Haiyang,Guan, Qirui,Hu, Haibin,Deng, Juean,Liu, Jun,Liu, Fengshou,Wu, Qing
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p. 6054 - 6062
(2012/10/30)
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- Kinetic studies on the stability and reactivity of β-amino alkylzinc iodides derived from amino acids
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(Chemical Equation Presented) β-Amino alkylzinc iodides are intrinsically unstable toward β-elimination and protonation. The aim of this study was to determine the rates of these processes and also to understand how the reactivity of a range of β-amino alkylzinc iodides in Negishi cross-coupling reactions is influenced by the presence of functional groups within the zinc reagent. Decomposition of β-benzamido alkylzinc iodides occurs by protonation, and the first-order rate constant for the self-protonation of the carbon-zinc bond in reagent 4b was determined to be 5.2 × 10-6 s-1 (at 291 K). In contrast, the carbamate derivative 2 decomposes by a first-order elimination process. The homologous reagent 3, derived from glutamic acid, decomposes more quickly by β-elimination, with a first-order rate constant of 24 × 10 -6 s-1 (at 291 K). Reagents 23 and 25, in which the Boc group has been replaced with a trifluoroacetyl group, are more stable toward β-elimination than the corresponding reagents 2 and 3, a striking outcome given that the trifluoroacetamido group is a better leaving group. Moreover, this replacement also changes the mechanism of the elimination to a second order process. Pseudo-second-order rate constants for the Negishi cross-coupling of reagents 2, 3, 23, and 25 with iodobenzene have been determined, revealing the higher reactivity of the glutamic acid-derived reagents 3 and 25. The main factor influencing reactivity, therefore, is determined to be the proximity of the ester group, rather than the nature of the nitrogen protecting group. Finally, β-amino alkylzinc iodides 46-48 containing Weinreb amides have been prepared, rate constants for their decomposition through elimination determined, and their synthetic potential for the preparation of β-amino ketones established.
- Rilatt, Ian,Jackson, Richard F. W.
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experimental part
p. 8694 - 8704
(2009/04/11)
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- Reactions of allyloxy(methoxy)carbene in solution. Carbene rearrangement and Claisen rearrangement of the carbene dimer
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Allyloxy(methoxy)carbene, with and without deuterium in the α-position of the allyloxy group, was generated in benzene at 50 and at 110°C. At the higher temperature, the carbene fragmented to allyl and methoxycarbonyl radicals that subsequently coupled. At the lower temperature, most of the carbene dimerised. The structure of the major product and the distribution of deuterium indicated that the dimer underwent Claisen rearrangement at 50°C to methyl 2-allyloxy-2-methoxy-4-pentenoate. Facile rearrangement of the dimer was supported by the results of a computation which placed the barrier at about 18 kcal mol-1.
- Plazuk, Damian,Warkentin, John,Werstiuk, Nick Henry
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p. 5788 - 5796
(2007/10/03)
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- Acylation of alkyl halides and amino aldehydes with a phosphane oxide-based d1-synthon
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Alkyl iodides and α-amino aldehydes can be homologated to the corresponding methyl esters and β-amino methyl esters, including β-amino-α-hydroxy methyl esters, using lithiated (dimethoxymethyl) diphenylphosphane oxide. The primary α,α-(dimethoxy) diphenylphosphane oxides obtained by this Horner-Wittig type process collapse to give the target esters under proton-catalyzed conditions in the presence of water. Detailed and carefully conducted mechanistic studies revealed that the diphenylphosphane oxide group is activated by protonation, and acts as the initial leaving group in this process. In the cases of adducts derived from the reaction of the phosphane oxide-stabilized anion with α-amino aldehydes, homologation to the β-amino- and β-amino-α-hydroxy methyl esters can be achieved by KOtBu-mediated elimination to the intermediate O,O-ketene acetals. These may either be allowed to react with water under acidic conditions to yield the β-amino methyl esters, or may be treated under the Sharpless asymmetric dihydroxylation conditions to directly furnish the β-amino-α-hydroxy methyl esters. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Bruenjes, Marco,Kujat, Christof,Monenschein, Holger,Kirschning, Andreas
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p. 1149 - 1160
(2007/10/03)
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- A convenient procedure for the synthesis of 1-tetralone dertivatives using a Suzuki coupling-Friedel-Crafts acylation sequence
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The reported 1-tetralone derivatives have been synthesized from arylbromides using as keys steps a Suzuki coupling followed by intramolecular Friedel-Crafts acylation.
- Esteban, Gemma,Lopez-Sanchez, Miguel A.,Martinez, Ma. Eugenia,Plumet, Joaquin
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p. 197 - 212
(2007/10/03)
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- Iron carbonyl-promoted isomerization of olefin esters to their α,β-unsaturated esters: Methyl oleate and other examples
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Ultraviolet photolysis of stoichiometric amounts of methyl oleate and Fe(CO)5 in hexanes solvent at 0°C gives Fe(CO)3(η4-α,β-ester) in which the α,β-unsaturated ester isomer of methyl oleate is stabilized by η4-oxadiene π coordination of the olefin and ester carbonyl groups to the Fe(CO)3 unit. Treatment of the Fe(CO)3(η4-α,β-ester) with pyridine or CO liberates the free α,β-ester, methyl octadec-trans-2-enoate, in 70% yield. The Fe(CO)3 unit both catalyzes the olefin isomerization and stabilizes the α,β-unsaturated ester, which results in the formation of the α,β-ester in a yield far above that (3.5%) observed for simple catalyzed methyl oleate isomerization. The much smaller olefin esters, methyl 3-butenoate and ethyl 4-methyl-4-pentenoate, are isomerized under the same conditions to their α,β-unsaturated esters in 94 and 90% yields, respectively. The effects of reaction conditions on the yield, the use of Fe(CO)3(cis-cyclooctene)2 as a nonphotolytic catalyst, and the mechanism of this useful synthetic process are discussed.
- Shih, Kuo-Chen,Angelici, Robert J.
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p. 7784 - 7792
(2007/10/03)
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- Ruthenium Complex-Catalyzed Carbonylation of Allylic Compounds
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Allylic alkyl carbonates are carbonylated under 40 atm of carbon monoxide at 100-120 deg C in the presence of a catalytic amount of Ru3(CO)12/1,10-phenanthroline to give α,β- or β,γ-unsaturated esters in good to high yields.For example, cinnamyl methyl carbonate afforded the corresponding β,γ-unsaturated esters, methyl trans-4-phenyl-3-butenoate (1) in 93percent yield.The regioselectivity in the carbonylation of crotyl methyl carbonate is unusual and it depends on the carbon monoxide pressure.The more sterically hindered carbon (γ-carbon) is predominantly carbonylated at 20-50 atm.When the reaction of cinnamyl methyl carbonate was performed at elevated temperature (150 deg C) without 1,10-phenanthroline, the dimer of 1, dimethyl 3-benzyl-2-(trans-2-phenylvinyl)glutarate, was obtained in 56percent yield.In the presence of secondary amines, allylic alkyl carbonates were carbonylated mainly at α-carbon to give α,β- or β,γ-unsaturated amides in high yields.
- Mitsudo, Take-aki,Suzuki, Nobuyoshi,Kondo, Teruyuki,Watanabe, Yoshihisa
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p. 7759 - 7765
(2007/10/02)
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- CHEMISTRY OF INDOLES CARRYING BASIC FUNCTIONS. PERT II. SYNTHESIS OF 4-SUBSTITUTED CYCLOHEPTINDOLES. A NEW ENTRY INTO THE RING SYSTEM
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Cycloheptindoles (7a), (7b), (12) were synthetized starting from 4-indoindole-3-carboxaldehydes (3a) and (3b).
- Moldval, Istvan,Szantay, Csaba,Szantay, Csaba
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p. 219 - 223
(2007/10/02)
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- CARBONYLATION OF 1,4-DI(CHLOROMETHYL)BENZENE AND ALLYL CHLORIDE IN METHANOL, CATALYZED BY DICOBALT OCTACARBONYL
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The effects of inorganic base on the yield and selectivity of carbonylation of 1,4-di(chloromethyl)benzene and allyl chloride, catalyzed by dicobalt octacarbonyl, in methanol with carbon monoxide at atmospheric pressure have been examined.The highest yields of products were obtained with K2CO3 and Na2CO3.Addition of MeI results in a considerable increase in yields in the presence of calcium bases, givimg dimethyl 1,4-phenylenediacetate, which in the absence of MeI is formed in appreciable amounts only in the presence of sodium carbonate.
- Terekhova, M. I.,Kron, T. E.,Petrova, N. E.,Petrov, E. S.
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p. 2101 - 2104
(2007/10/02)
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- Reactions of π-allylic complexes of palladium with methyl formate
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The reaction of methyl formate with various π-allylic palladium complexes is reported. Unsaturated carboxylic acid esters are formed in high yield and selectivity. A comparison of the reactivity of methyl formate with that of the hydroesterification subst
- Keim,Becker,Kraneburg,Greven
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- KINETIC RESOLUTION OF RACEMIC β,γ-EPOXY ESTERS WITH PIG LIVER ESTERASE (PLE, E.C. 3.1.1.1.)
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The β,γ-epoxy esters (+/-)-2 to (+/-)-6 were synthetisized.The E-values of kinetic resolution of 2, 3, 4, and 6 with PLE and the absolute configuration of the products of the hydrolysis were determined by the conversion to known compounds.
- Mohr, Peter,Roesslein, Lukas,Tamm, Christoph
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p. 2513 - 2516
(2007/10/02)
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- Maximally Inhibited Pyrolysis Kinetcs of Bromo Esters in the Gas Phase. The Ion Pair Mechanism
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The kinetics of the pyrolyses of two bromo esters have been investigated in a static system over the temperature range 379-419 deg C and pressure range 51-110 Torr.The reactions in seasoned vessels, and under maximum inhibition with the radical chain suppressor propene, are homogeneous, unimolecular, and follow a first-order rate law.The Arrhenius equations for these elimination processes were found to be as follows: for methyl 4-bromobutyrate, log k1 (s-1) = (13.38 +/- 0.59) - (216.7 +/- 7.6)kJ mol-1 (2.303RT)-1; for methyl 5-bromovalerate, log k1 (s-1) = (13.83 +/- 0.17) - (228.9 +/- 2.3) kJ mol-1 (2.303RT)-1.The anchimeric assistante of the carbomethoxy substituent is determinant in the elimination process, where dehydrobromination product and lactone formation result from an intimate ion pair type of mechanism.The partial rates toward each of the primary products have been determined, reported, and discussed.The present work provides further support of the intimate ion pair mechanism in the gas-phase pyrolysis of special types of organic halides.
- Chuchani, Gabriel,Dominguez, Rosa M.
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p. 1883 - 1887
(2007/10/02)
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- Lewis Acid Catalysis of Photochemical Reactions. 5. Selective Isomerization of Conjugated Butenoic and Dienoic Esters
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The effects of Lewis and Broensted acids upon the photoisomerization reactions of several conjugated butenoic and dienoic esters have been investigated.Lewis acid inhibit the photochemical deconjugation of α,β- to β,γ-unsaturated butenoic esters and shift the photoequilibrium between E and Z isomers toward the Z isomer.As such, irradiation of E α,β-unsaturated esters in the presence of EtAlCl2 provides a convenient method for the preparation of the thermodynamically less stable Z isomer.Irradiation of methyl (E,E)-2,4-hexadienoate and methyl (E,E)-5-phenyl-2,4-pentadienoate in the absence of added catalysts results in nonselective E,Z isomerization to give mixtures of all four stereoisomers in roughly comparable yields.In the presence of the Broensted acid trifluoroacetic acid, quantitative conversion of methyl 2,4-hexadienoates to methyl 3,4-hexadienoate is observed.The acid serves as a catalyst for the thermal 1,3-hydrogen shift of an allenic enol ester formed via a photochemical 1,5-hydrogen shift of the conjugated esters.Irradiation of the ground-state complexes of the conjugated esters with the Lewis acids EtAlCl2 or BF3 results in selective E,Z isomerization about the α,β-double bond in methyl 2,4-hexadienoate and the γ,δ-double bond in methyl 5-phenyl-2,4-pentadienoate.The mechanistic bases for the observed effects of Lewis acids are selective excitation of the more strongly absorbing E complex and more efficient isomerization of the excited E vs.Z complex.
- Lewis, Frederick D.,Howard, Daniel K.,Barancyk, Steven V.,Oxman, Joe D.
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p. 3016 - 3023
(2007/10/02)
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- Carbonylation of Organomercury Compounds: A General Synthesis of Carboxylic Acids and Esters
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Organomercury compounds react with carbon monoxide in aqueous or alcoholic media to give good yields of carboxylic acids or esters.The carboxyl group is introduced selectively at the site of the carbon-mercury bond.Homogeneous group 9 and 10 metal complexes catalyze this carbonylation reaction, which yields mercury(0) as the inorganic byproduct.The mercuration-carbonylation sequence represents a general synthesis of carboxylic acids and esters.
- Baird, William C.,Hartgerink, Ronald L.,Surridge, John H.
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p. 4601 - 4605
(2007/10/02)
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- A VERSATILE ROUTE TO MIXED VINYLKETENE ACETALS : USE OF 1-t-BUTYLDIMETHYLSILOXY-1-ETHOXY BUTADIENE IN CYCLOHEXENONE SYNTHESIS
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The successful entry to the diverse mixed vinylketene acetals 3 extends the participation of these intermediates in cyclohexenone synthesis.
- Lombardo, Luciano
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p. 381 - 384
(2007/10/02)
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- On the Conjugative Isomerizations of β,γ-Unsaturated Esters. Stereochemical Generalizations and Predictions for 1,3-Prototropic Shifts under Basic Conditions
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An investigation of the base-catalyzed conjugative isomerization of a series of β,γ-unsaturated esters to their corresponding α,β-unsaturated esters was performed.It was found that, withh sodium hydride in THF, methyl 3-butenoate isomerized initially to a 5:1 ratio of (Z)- to (E)-methyl 2-butenoates; the Z:E ratio is time dependent, and after several days, the thermodynamic ratio 1:23 = Z:E was obtained.The isomerization appears to be catalytic in NaH, as it proceeds with less than 1 molar equiv of base, no hydrogen evolution is observed, and the reaction rate is approximately first order in NaH and zero order in ester.Under the same conditions (Z)-methyl 3-hexenoate isomerized stereoselectively to (E)-methyl 2-hexenoate while (E)-methyl 3-hexenoate isomerized to a 2:1 mixture of (Z)- and (E)-methyl 2-hexenoates.These product ratios are far from the isomeric compositions obtained under equilibrating conditions.To investigate further the stereochemical outcome of these isomerizations, three isomeric β,γ-unsaturated methyl esters were studied: (a) methyl 3-ethyl-3-butenoate isomerized exlusively to (E)-methyl 3-methyl-2-pentenoate; (b) (E)-methyl 3-methyl-3-pentenoate isomerized exlusively to (Z)-methyl 3-methyl-2-pentenoate; (c) (Z)-methyl 3-methyl-3-pentenoate isomerized exlusively to (E)-methyl 3-methyl-2-pentenoate.In the latter three cases, dimerization was not observed presumably due to steric effects.Related results were observed for a smaller series of β,γ-unsaturated amide isomerizations.Examination of the literature on olefin isomerizations reveals a general trend that the current results exemplify.Thus, in the absence of severe steric factors or cation-anion complexation, deprotonation at allylic positions kinetically preferentially forms the anion possessing a cisoid crotyl subunit (if available) regardless of initial substrate conformation.The stereochemical consequences of this results in E Z and Z E geometry conversions in kinetic 1,2-transpositions of olefins.This generalization can also be applied to the stereochemical results of ketone, ester, and hydrazone enolate formation, base-catalyzed exchange in polysubstituted aromatics and heteroaromatics, and other reactions involving the formation of allylic or benzylic anions.
- Alcock, Simon G.,Baldwin, Jack E.,Bohlmann, Rolf,Harwood, Laurence M.,Seeman, Jeffrey I.
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p. 3526 - 3535
(2007/10/02)
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- REACTIONS OF KETENE ACETALS-14; THE USE OF SIMPLE MIXED VINYLKETENE ACETALS IN THE ANNULATION OF QUINONES
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α,β- and β,γ-unsaturated esters can be converted by strong base and chlorotrimethylsilane to the corresponding mixed vinylketene acetals which are shown to be particularly useful and generally applicable reagents for the regiospecific annulation of halogenoquinones.The reaction proceeds readily with a variety of substrates including benzoquinones.
- Savard, Jacques,Brassard, Paul
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p. 3455 - 3464
(2007/10/02)
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- ZINC (0) MEDIATED REGIO AND STEREOSELECTIVE COUPLING OF SUBSTITUTED BROMOCROTONATES
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A useful synthetic approach to 5-carbomethoxy-hepta-2,6-dienoates is reported, formally via Michael reaction with inverse electron demand.
- Orsini, F.,Pelizzoni, F.
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p. 169 - 178
(2007/10/02)
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- Preparation of esters
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β,γ-Unsaturated esters are prepared by the reaction of the corresponding β,γ-unsaturated carbonate with carbon monoxide in the presence of a group VIII metal catalyst.
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- The Synthesis of Specifically and Selectively Deuteriated 4,4'-Bisalkoxyazoxybenzene Derivatives
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In connection with deuterium n.m.r. studies of molecular motion in liquid crystals we have developed a number of methods for the synthesis of selectively deuteriated 4,4'-bisalkoxyazoxybenzenes.This paper is concerned with (i) the labelling of specific methylene segments of the alkoxy-chains, (ii) the labelling of the aromatic nucleus, and (iii) the selective enrichment of the deuterium content of one alkoxy-chain relative to the other.Our studies of the n.m.r. spectra of these liquid crystals have shown that there is not (as has sometimes been supposed) a monotonic decrease in C-D quadrupole splitting in passing from the oxygen to the CD3 end of the alkoxy-chain.In -PAA (p-azoxyanisole) we have also shown that the smaller splitting is associated with the CD3O group nearest to the NO end of azoxy-group.Whereas the photorearrangement of azoxy-compounds is normally regiospecific, the photorearrangement of PAA selectively deuteriated in one methoxy-group is unusual in that it leads to isotopically scrambled products.
- Boden, Neville,Bushby, Richard J.,Clark, Leslie D.
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p. 543 - 551
(2007/10/02)
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- Esterification of Carboxylic Acids Mediated by Chlorotrimethylsilane
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The reaction of aliphatic and aromatic carboxylic acids with alcohols in presence of chlorotrimethylsilane affords, under mild condition, the corresponding esters in excellent yields.The reaction can be extended to amino acids which also yield the amino esters in high yields.
- Mandal, Arun K.
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- Process for preparing unsaturated aliphatic esters
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This invention relates to the carbonylation of unsaturated aliphatic halides by the insertion of carbon monoxide into the carbon-halogen bond of said unsaturated aliphatic halide, in the presence of a hydroxylated coreactant, to form an unsaturated, halogen-free, aliphatic ester, using as catalyst homogeneous noble metal complexes with Group VB donor ligands in combination with Group IVB metal halides.
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